1. The Field of the Invention
The present invention concerns on-line statistical analysis of microwave determination of the gas fraction in three phase mixtures of oil, water and gas.
2. The Prior Art
There presently are no instruments making only two measurements and using statistical methods capable of predicting the ratios of oil, water and gas in a multiphase stream. The TEXACO STARCUT.RTM. monitor described in U. S. Pat. Nos. 4,499,418 and 4,947,127, the disclosures of which are incorporated herein by reference, is enhanced by the present invention to allow prediction of the ratios of oil, water and gas. There are many applications where a three-phase water cut monitor which does not require separation of the fluid phases will save millions of dollars in construction costs by obviating the requirement for a three-phase separation facility. Furthermore, experience shows that gas (and therefore errors in instruments not insensitive to gas) is present to some extent in virtually all live crude oil handling operations. For example, in primary well head production situations, even if no gas is expected initially, gas will surely result due to pipeline pressure drops and with aging of the reservoir. The choice of a low gas water cut monitor can save the cost of constructing three phase and even two phase separation facilities.
Field experience has shown that all known instruments designed to determine water fraction are sensitive to the presence of gas in the flowing mixture. The presence of gas tends to reduce the reading of water fraction, even though the actual water fraction has not changed. Experience has also shown that gas is usually present in live crude handling pipelines. It has therefore been a high priority to develop methods of reducing the effects of gas on water cut monitors.